In certain industries, particularly in the nuclear and chemical fields, and in situations such as the repair of pipes on board a ship underway, pipe systems are repaired by welding or brazing. This welding or brazing must take place in an atmosphere which is free of contaminates from the pipe interior. Additionally, the welding or brazing often requires the presence of an inert atmosphere, especially for tungsten inert gas welding wherein the work area must be free of a chemically reactive atmosphere containing water vapor and oxygen. The chemically reactive atmosphere is displaced by inert gas such as argon or helium.
Conventional systems for repairing pipes involve the use of valves, plugs and pigs. These conventional devices are designed with the intention of completely stopping the flow of fluid through the pipe at a specific location in order to permit work at such location without contamination from the fluid conveyed through the pipe. These devices are disadvantageous in that they are not always able to completely stop the flow of fluid through the pipe, they require significant amounts of labor time to adjust and regulate them and they are difficult to manufacture, maintain and operate.
The most significant disadvantage is that an inferior joint is produced during the repair operations if the stoppage of pipe fluid is not complete and the fluid leaking through to the work area adversely affects the brazing or welding at the repair area. The inferior weld joints formed with the conventional devices are often not discovered to be unsatisfactory until subjected to pressure or subjected to radiographic or ultrasonic inspection. Additionally, these inferior joints result in additional expenses caused by reworking, plant down time, engineering review and, if necessary, application to the customer for acceptance of an inferior joint.
The flow of fluid past a seal is proportional to the pressure differential across the seal and inversely proportional to the resistance offered by the seal. The conventional valves, plugs and pigs, in attempting to halt all flow through a pipe, permit pressure to build up and cause leakage about the seal as a result of the pressure build up.
A typical example of a pipe line plugging system is disclosed in U.S. Pat. No. 4,077,435 to Van Scoy. The system disclosed in the Van Scoy patent suffers rom the deficiencies noted above. Additionally, this system is disadvantageous in that it requires substantial modification of the existing pipe system in order to permit its operation and does not have means for providing purge gas in the work area. Moreover, the Van Scoy system requires complete shutdown of the pipe system during repair work.
Conventional devices for repairing relatively small, household pipe systems are disclosed in U.S. Pat. No. 2,322,842 to French and U.S. Pat. No. 2,753,876 to Kurt. The French device includes a hollow tube with an expandable seal actuated by a mechanical screw mechanism. The end of the tube opposite the seal is provided with a valve to control the flow of fluid through the pipe, which valve is closed during repair of the pipe to halt fluid flow. The Kurt patent discloses a drain plug valve flushing device having an expandable body member which is expanded when flushing fluid flows through the device to prevent back flow of the flushing fluid in the pipe. The system of the French or Kurt patents would not be effective for use in an industrial pipe system since the seal would not be adequate, the systems do not have a mechanism to supply purge gas to the work area and they are otherwise not adaptable to the industrial environment.